Behaviour of radiogenic Pb in zircon during ultrahigh-temperature metamorphism: an ion imaging and ion tomography case study from the Kerala Khondalite Belt,southern India

Zircon crystals from a locally charnockitized Paleoproterozoic high-K metagranite from the Kerala Khondalite Belt (KKB) of southern India have been investigated by high-spatial resolution secondary ion mass spectrometry analysis of U–Th–Pb and rare earth elements (REE), together with scanning ion imaging and scanning ion tomography (depth-profiled ion imaging). The spot analyses constrain the magmatic crystallization age of the metagranite to ca. 1,850 Ma, with ultrahigh-temperature (UHT) metamorphism occurring at ca. 570 Ma and superimposed charnockite formation at ca. 520–510 Ma, while the ion imaging reveals a patchy distribution of radiogenic Pb throughout the zircon cores. Middle- to heavy-REE depletion in ca. 570 Ma zircon rims suggests that these grew in equilibrium with garnet and therefore date the UHT metamorphism in the KKB. The maximum apparent ²⁰⁷Pb/²⁰⁶Pb age obtained from the unsupported radiogenic Pb concentrations is also consistent with formation of the Pb patches during this event. The superimposed charnockitization event appears to have caused additional Pb-loss in the cores and recrystallization of the rims. The results of depth-profiling of the scanning ion tomography image stack show that the Pb-rich domains range in size from <5 nm to several 10 nm (diameter if assumed to be spherical). The occurrence of such patchy Pb has previously been documented only from UHT metamorphic zircon, where it likely results from annealing of radiation-damaged zircon. The formation of a discrete, heterogeneously distributed and subsequently immobile Pb phase effectively arrests the normal Pb-loss process seen at lower grades of metamorphism.     

Interaction of the Atmosphere and Lithosphere in the Minute Range of Periods

Doklady Earth Sciences - The interaction between the atmosphere and the lithosphere in the minute range of periods is considered. The technique of assessment of the influence of atmospheric...     

New data on the most ancient early quaternary glaciation in Gornyi Altai

The data presented in this work introduce substantial corrections into the Upper Cenozoic stratigraphy and geological history of Gornyi Altai. They provide evidence for the most ancient Early Pleistocene glaciation in this region. This follows from finds of faceted boulders buried in the Bashkaus Formation. Pale-omagnetic investigations revealed in the latter a wide zone of negative polarity corresponding to the Matuyama Chron in the magnetostratigraphic scale and made it possible to correlate the formation with the Lower Pleistocene in the standard stratigraphic scale. It is shown that global cooling at the beginning of the Quaternary Period stimulated development of glaciation on the southern slope of the Kuraiskii Range exceeding in size its present-day scale.     

A new type of noble metal mineralization in the Northern Caucasus

The weathering crust of the Beden ultrabasite massif (the basin of Big Laba River) is identified and studied. Anomalously high contents of noble metals (Au, Pt, Pd) are revealed in the basal horizon of the Jurassic part of the weathering crust. For this reason we suspect an existence of a belt of noble metal miner-alization in the Paleozoic ultrabasites in the Peredovoi Range of the Northern Caucasus.     

Titan's surface at 2.2-cm wavelength imaged by the Cassini RADAR radiometer: Calibration and first results

The first comprehensive calibration and mapping of the thermal microwave emission from Titan's surface is reported based on radiometric data obtained at 2.2-cm wavelength by the passive radiometer included in the Cassini Radar instrument. The data reported were accumulated from 69 separate observational segments in Titan passes from Ta (October 2004) through T30 (May 2007) and include emission from 94% of Titan's surface. They are diverse in the key observing parameters of emission angle, polarization, and spatial resolution, and their reduction into calibrated global mosaic maps involved several steps. Analysis of the polarimetry obtained at low to moderate resolution (50+ km) enabled integration of the radiometry into a single mosaic of the equivalent brightness temperature at normal incidence with a relative precision of about 1 K. The Huygens probe measurement of Titan's surface temperature and radiometry obtained on Titan's dune fields allowed us to infer an absolute calibration estimated to be accurate to a level approaching 1 K. The results provide evidence for a surface that is complex and varied on large scales. The radiometry primarily constrains physical properties of the surface, where we see strong evidence for subsurface (volume) scattering as a dominant mechanism that determines the emissivity, with the possibility of a fluffy or graded-density surface layer in many regions. The results are consistent with, but not necessarily definitive of a surface composition resulting from the slow deposition and processing of organic compounds from the atmosphere.     

Book reviews

APPLIED GEOGRAPHY: Issues, Questions and Concerns (Geo Journal Library Vol. 15) edited by M. S. Kenzer. 16 × 24 cm, x and 210 pages. Kluwer: Dordrecht 1989 (ISBN 0 7923 04381).

WINE AND THE VINE: An Historical Geography of Viticulture and the Wine Trade by T. Unwin. 16 × 24 cm, xvi and 409 pages. Routledge: London 1991 (ISBN 0 415 13120 6) $A155.00 (hard); distributed by The Law Book Co.

WATERFRONT SYDNEY 1860–1920 by G. Aplin and J. Storey. 26 × 18 cm. 144 pages. Allen & Unwin: Sydney 1991 (first published 1984) (ISBN 1 86373 098 2) $A24.95 (soft).

Australian Geographer 23 (2), November 1992

INDUSTRIAL LOCATION: Principles and Policies (Second Edition) by K. Chapman and D. F. Walker. 15 × 23 cm, xiii and 322 pages. Basil Black‐well: Oxford 1991 (ISBN 0 631 16789 7) $A39.95 (soft).

INTERNATIONALISATION OF AUSTRALIA'S SERVICE INDUSTRIES by J. V. Langdale. 17 × 25 cm, iv and 373 pages. Australian Government Publishing Service, for Department of Industry, Technology and Commerce: Canberra 1991 (ISBN 0 644 13841 6).

TOURISM AND GOLD IN KAKADU: The Impact of Current and Potential Natural Resource Use on the Northern Territory Economy by B. Knapman, O. Stanley and J. Lea. 21 × 29 cm, vi and 49 pages. North Australia Research Unit, Australian National University: Darwin 1991 (ISBN 0 7315 1179 4).

ABORIGINAL AUSTRALIA AND THE ‘NEW FEDERALISM’ INITIATIVE (Discussion Paper No. 2) by G. J. Crough. 14 × 21 cm, 42 pages. North Australia Research Unit, Australian National University: Darwin 1991 (ISBN 0 7315 1325 8).

AUSTRALIAN NATIONHOOD AND OUTBACK INDIGENOUS PEOPLES (Discussion Paper No. 1) by P. Jull. 14 × 21 cm, 38 pages. North Australia Research Unit, Australian National University: Darwin 1991 (ISBN 0 7315 1309 6).

MIGRATION AND DEVELOPMENT IN THE SOUTH PACIFIC (Pacific Research Monograph No. 24) edited by J. Connell. 17 × 25 cm, xii and 199 pages. National Centre for Development Studies, Australian National University: Canberra 1990 (ISBN 0 07315 0668 5) $A25.00 (soft).

POPIULESIN BLONG HONIARA: Olketa Popiulesin Map Blong 1986 Sensis. HONIARA: 1986 Census Atlas (Statistics Office Occasional Paper No. 4 / Board of Development Studies Monograph No. 1) by A.C. Walsh. 21 × 29 cm, vii and 95 pages. Department of Statistics: Honiara and Board of Development Studies, Massey University: Palmerston North 1990 (ISSN 0114 8834) $NZ34.00 in New Zealand, $NZ38.00 elsewhere (soft).

DOI MOI: Vietnam's Renovation Policy and Performance (Political and Social Change Monograph No. 14) edited by D. K. Forbes, T. H. Hull, D. G. Marr and B. Brogan. 15 × 22 cm, xiv and 263 pages. Department of Political and Social Change, Australian National University: Canberra 1991 (ISBN 0 7315 1303 7).     

The nonlinear solar dynamo and differential rotation: A Taylor number puzzle?

We consider dynamically consistent mean-field dynamos in a spherical shell of incompressible fluid. The generation of magnetic field and differential rotation is parameterized by the - and -effects, respectively. Extending previous investigations, we include now the cases of moderate and rapid rotation in the sense that the inverse Rossby number can approach or exceed unity: This can lead to disk-shaped -contours, which are in better accordance with recent results of helioseismology than cylindrical -contours. On the other hand, in order to obtain -dynamo cycles the Taylor number has to be so large, that eventually cylindrical -contours become unavoidable (cf. Taylor-Proudman theorem). We discuss the different possibilities in a state diagram, where the inverse Rossby number and the relative correlation length are taken as the elementary parameters for mean-field dynamos.